INPUT DEVICES
are peripheral devices designed to get data into the computer in machine- readable form. They accept the data from outside the computer and transmit it to CPU. Different input devices have been developed to make data input as efficient as possible. Input devices are categorized as follows: *v Key Input *v Point and Draw *v Source Data Automation *'Key input devices' The Keyboard One input device you will probably have to learn to use is the keyboard. The keyboard converts letters, numbers and other characters into electrical signals that are machine- readable by the computer’s processor. The keys on the computer keyboard are often classified as alphanumeric keys (letters and numbers), punctuation keys (comma, period, semicolon and so on). Most keyboards have four main parts namely: v The alphanumeric keypad is very similar to a standard typewriter keyboard. Depending on the computer, some alphanumeric keys have other uses than those related to typing. There may also be some special keys such as Pause Break and Print Screen. v The Control keys '''control the symbol that marks your position on the monitor. You use a cursor control key to move the cursor in the direction of the arrow that is pressed. v The '''Function keys '''are located at the top of the keyboard above the alphanumeric keypad. They are used to activate specific commands that the computer system can perform. These commands are different depending on the program that is being used. Many programs come with a plastic or cardboard device called a template. The template fits over the function keys to remind you which key to press for each command. v The '''numeric keypad '''has keys for each of the ten Arabic digits and is usually set up like a calculator. Keyboards are divided into two basic types, the '''traditional alphanumeric keyboard and the''' special-function keyboard. ' q '''Alphanumeric Keyboards ' QWERTY Layout ' The QWERTY layout (pronounced KWEHR-tee) for our typewriter keyboard comes from the first six letters in the top alphabet row. It is also called the “Universal” keyboard for rather obvious reasons. It was the work of inventor Christopher L. Sholes, who put together the prototypes of the first commercial typewriter in a Milwaukee machine shop back in the 1860’s. '''Advantages of Keyboard ' v Reliable for data input of text and numbers. v Usually supplied with a computer so no additional cost. v Specialized keyboards are available. 'Disadvantages of Keyboard ' v Users may be slow or not very accurate typists. v Slow for accessing menus etc. and difficult to use if you want to move objects around the screen. v Difficult for people unable to use keyboards through paralysis or muscular disorder. v Causes Carpel Tunnel Syndrome, which is painful, and disabling disorder caused from inflammation and swelling in the tendon that runs through the narrow carpel tunnel wrist. ' ' q 'Specialized Keyboards ' Braille keyboards This is a special keyboard which has letters raised in Braille on them for blind people to use. 'Advantages of Braille keyboard ' v Available for people with disabilities that don’t let them use a mouse or a trackball. v Similar to the QWERTY layout keyboard. '''Disadvantages of Braille keyboard v Need special training to use some. v Use only by blind people. Retail keyboards ''' Some keyboards are designed for specific applications. For example the cash register like terminals at most fast-food restaurants have special-purpose keyboard. The retail keyboard shown below has pointing device and barcode reader. '''Point and Draw Devices A point and draw device can be used to point to select (click) a particular user option, and can also be used to draw. The Mouse ' The mouse is normally used along with a keyboard. Whenever the mouse is moved the mouse pointer on the desktop move accordingly. It can be position anywhere on the screen. A mouse has two or three buttons. The following are three basic operations of the mouse:- '''Click-' you tap or click the left mouse button once to select a menu item or a program represented by an icon. 'Double click-' This is the tapping of the mouse button twice in quick successor 'Dragging-' Press and hold the left mouse button to drag the mouse cursor across the screen. The mouse usually has a cable that is connected (by being plugged into a special port or socket) to the microcomputer’s system unit. This tail-like cable and the rounded “head” of the instrument are what suggested the name mouse. Some newer mouse types are wireless (cordless), that is they use battery-powered senders to send infrared signals to a battery-powered receiver hooked up to serial port on the back of the computer. There are three basic types of mice: '''Mechanical: This has a rubber or metal ball on its underside that can roll in all directions. Mechanical sensors within the mouse detect the direction of the ball is rolling and move the screen pointer accordingly. Optomechanical: Same as mechanical mouse but uses optical sensors to detect motion of the ball. Optical: Uses a laser to detect the mouse’s movement. You can move the mouse along a special mat with a grid so that the optical mechanism has a frame of reference. Optical mice have no mechanical moving parts. They respond more quickly and precisely than mechanical mice, but they are also more expensive. The mouse is still the most popular point and draw device, but this could change in future. Advantages of the Mouse ''' v Ideal for use with desktop computers. v Usually supplied with a computer so no additional cost. ' v All computer users tend to be familiar with using them.' ' '''Disadvantages of the Mouse ' v They need a flat space close to the computer. v The mouse cannot easily be used with laptop, notebook or palmtop computers. (These need a tracker ball or a touch sensitive pad called a touch pad). Light Pen ' The Light Pen is a hand held pen-shaped device. It senses marks or other indicators through a light sensitive cell in its tip. The display identifies the position of the pen when it is placed close to the screen. One feature of some light pens is the buttons that a user can press to move back and forth on pages that are stored. Engineers, graphic designers and illustrators use light pens. '''Advantages of Light Pen ' v Able to draw on the screen. v Easy to select options from menu presented on the screen. v Gives the user the full range of mouse capabilities, without the use of a pad or any horizontal surface. v Can be used on any size screen. v Users can interact more with application, in such modes as drag and drop, or highlighting. 'Disadvantages of Light Pen ' v Very inaccurate v Tiring to use v User must lift the pen for use 'Joystick ' This is a pointing device that consists of vertical handle like gearshift lever mounted on a base with one or two buttons. The physical movement on a computer screen of an object or of another device to which the processor is connected. For example, it allows you to steer a car in computer or check the size of a machine tool part using a computer-controlled measuring machine. You may find that the cursor keys on the keyboard are often used instead of a joystick. This input device often supports computer games and computer-aided design (CAD) work. Small joysticks called track point devices are sometimes built into keyboards of portable computers and used instead of am mouse. 'Advantages of Joystick ' v A favourite in arcades v Available for use by people who have disabilities that don’t let them use a mouse 'Disadvantages of Joystick ' v Moves only in direction the cursor stick is pushed. v In order for the printer to be stopped joystick must be returned to an upright position. 'Touch Screen ' The touch screen is designed to allow a finger to be used to active on screen commands. People who are not computer literate often use this. 'Advantages of Touch Screen ' v Person with limited or no computer knowledge of the keyboard will find this system very useful. v Software can alter the screen while it is running making it more flexible than a printed overlay keyboard. v No extra peripherals are needed apart from the touch screen monitor itself 'Disadvantages of Touch Screen ' v Not suitable` for inputting large amounts of data v Selecting detailed objects can be difficult with fingers v Touching the screen leaves a smudge. The screen has to be clean often in order not to present a dirty appearance. v Some touch screen use an overlay that can affect the quality of the image. 'Trackball ' The trackball is a ball mounted in a box that, when moved, results in a similar movement of the cursor on a display screen. Some people refer to the trackball as an upside-down mouse with a bigger ball. 'Advantages of Trackball ' v Ideal for use where flat space close to the computer is limited. v Can be useful with laptops as they can be built into the computer keyboard or clipped on. v Large amount of arm movement not required. v Sensitivity can be altered to allow more accurate targeting. 'Disadvantages of Trackball ' v Not supplied as standard so an additional cost and users have to learn how to use them. v Wrist is bent during use v Requires more finger movement, so finger tire easily. v Requires a lot of work to do large movements of the cursor 'Digitizer Tablet or Digitizing Pad ' The co-ordinates on the digitizing tablet correspond to those on the computer’s screen. The tablet uses a pen-like stylus. The tablet is used to do the drawing and sketches of images; when the drawing is complete it is stored in a digital form and you can recall it at any time. Used for artwork and Computer Aided Design (CAD). 'Advantages of Digitizer Tablet or Digitizing Pad ' v Very accurate v Allows shading and many other effects similar to those artists achieve with pencil, pen or charcoal. v Allows the storage of hand-written messages, which can be stored electronically. Disadvantages of Digitizer Tablet or Digitizing Pad v If pad is damaged the tablet is unable to function as intelligence is in the pad. v Each point on the tablet represents a point on the display in a fixed manner. 'Source Data Automation Input Devices ' Source Data Automation is when data is collected at the source and entered directly into the computer system without the need for key transcription. The use of source data automation eliminates the duplication effort, and the potential for errors. '''Scanners These are used to digitize images of pages or objects. A light moves slowly over the surface of the picture or object to be scanned. The colours of the reflected light are detected and digitized to build up a digital image. The digital data can be saved by a computer as an image file. Advantages of Scanner ' v Flatbed scanners are very accurate and can produce images with a far higher resolution than a digital camera. v Able to make exact duplication of an original document. '''Disadvantages of Scanner ' v Can produce very large image files, which need a lot of computer memory to view and edit. v Not all characters or images are always recognized and scanned correctly. ' ' 'Digital Camera ' These are used to take photographs like a normal camera but produce digital images instead of using film. The light passing through the lens is digitized by special '''light sensitive sensors. The image is stored on memory chips in the camera and can then be transferred to a computer. The resolution of such cameras is increasing rapidly and professional models have become standard in photo-journalism. Images are usually compressed, as jpeg’s to save memory. Advanced models have removable memory cards to increase the camera’s storage capacity. Images can be transferred to a computer by cables or memory card readers. Advantages of Digital Camera ' v No film is needed and there are no film developing costs. v Unwanted images can be deleted straight away. v Images are already digital and can easily be transferred to a computer and edited or transferred over the internet. v Special image editing software can allow a huge range of adjustments and special effects to be tried. '''Disadvantages of Digital Camera ' v Resolution is still not as good as film but is improving steadily v Images often have to be compressed to avoid using up too much expensive memory. ' ' 'Microphone ' This is used for the input of sound, which is then digitized by the computer. Voice recognition software can be used to convert your voice into text or to control menu options. 'Video Digitizer ' A video digitizer is used to convert analogue signals from a video camera or videocassette recorder into a digital format. The '''digitized video data can then be saved as a file or played on the screen. Software will allow the video to be edited and special effects added, as well as individual still images to be captured and saved. Many modern video cameras save the data in a digital format anyway so a video digitizer would not be needed. ' ' Midi Instruments ' These are used to produce music and are normal musical instruments, which have a midi port for input into a midi interface in the computer. They often have a wide range of special effects or stored sound data from real instruments. Specialized software allows the digitized music data to be stored as a file, displayed on screen and edited ready for playback. '''Sensors ' These detect changes in the physical or chemical environment and convert them into electrical signals. These signals can then be digitized and used by the computer. There are a huge range of possible sensors and they include: heat; light; sound; movement; magnetism; pressure; strain; acidity (pH); oxygen levels; liquid levels; humidity; pulse rates; salinity; water flow; speed and acceleration. Switch sensors can detect angles of tilt or whether something is open or closed. Sensors are often used when '''data logging. Advantages of Sensor ' v Regulate the temperature in green. v Regulates the flow of traffic build up and bundles. v Regulate the temperature in a furnace. '''Disadvantages of Sensor ' v Causes serious traffic build up and accidents when out of order. v Causes plants to die when malfunctioning. v Cause air accidents when malfunctioning. ' ' 'Barcode Reader ' A bar code is a made up vertical lines (bars) and spaces. The sequence of bars and spaces of different thickness represents a sequence of numbers. Bar codes are commonly found on packaging and the code gives information about the country of manufacture, the name of the manufacturer and the product itself. A bar code reader is used to read the code. The reader uses a laser beam that is sensitive to the different reflections from the lines and the spaces. The reader translates the reflected light into digital data that is transferred to a computer for immediate action or storage. Bar codes and readers are most often seen in supermarkets and retail stores, but a large number of different uses have been found for them. They are also used to take inventory in retail stores; to check out books from a library; to track manufacturing and shipping movement; to sign in on a job; to identify hospital patients; and to tabulate the results of direct mail marketing returns. 'Advantages of Barcode Reader ' v It allows for faster more accurate checkout and inventory control. v Eliminates the human element thus reduces errors. 'Disadvantages of Barcode Reader ' v Input is limited to a number code. v Collection of data entry must be close to source. 'Optical Character Recognition (OCR) ' This uses an ordinary scanner to take a digital image of printed or even hand-written text. The OCR software then converts then image of the text into an actual text file by recognizing each character. The text file can then be edited using a word processor. OCR is also used to automatically recognize postcodes on letters at sorting offices. 'Optical Mark Reader (OMR) ' Similar to a bar code reader but uses infra-red light to scan marks on prepared forms such as multiple choice examination answer sheets or lottery tickets. The infrared light is not reflected when it scans over a mark and the position of the mark is passed back to the computer. The software then matches up the position of the mark with the information on the sheet. This provides a very fast and accurate method of inputting large amounts of data, provided the marks have been mage accurately and clearly. 'Magnetic Ink Character Recognition ' This uses special ink, which contains iron particles that can be magnetized and then read when the printed numbers passes through a MICR reading machine. The MICR reading machine will only recognize numbers printed in a standard font the magnetic ink. This provides a high level of security because any attempt to alter the magnetic ink printout with normal ink will be ignored. Because it is expensive, MICR it is mainly used by banks. The account number, the cheque number and the branch number are '''pre-printed on a cheque. When you receive a cheque and deposit it in your bank they print the amount '''and '''your account details on the cheque in magnetic ink. It then sent to a clearing bank to be read by another MICR reading machine and the correct amounts are automatically transferred between accounts by computers. Advantages of MICR ' v Provides a high level of security. v Able to be read by the machine even when the cheque is bent. '''Disadvantages of MICR ' v Expensive to acquire ' v Ink and ink eraser is very expensive' ' v Not yet sophisticated enough to read hand-written text accurately.' ' ' ' '''Magnetic Stripe Reader ' Magnetic stripes are thin strips of magnetic tape, which are usually found on the back of plastic credit and debit cards. When the card is inserted into a reader (in an Automatic Teller Machine or ATM for example) the tapes slides past a play back head similar to that used in a tape recorder. This reads the data from the stripe and passes it to a computer. Advantages of Magnetic Stripe Reader v Simple to use and cheap to produce. v The data can be altered if necessary. Disadvantages of Magnetic Stripe Reader v Very limited storage capacity. v Data easily destroyed by strong magnetic fields. v Nit secure as thieves can obtain the readers and alter the data.